This invention relates to the processing of product gases obtained by pressure gasification of finely divided (pulverulent)fuels.
More particularly, the invention relates to a method of processing gases of the type mentioned above to cool them, at least in part scrub them of entrained dust and saturate them with water vapor.
The invention also relates to an apparatus for carrying out the method.
When pulverulent solid fuel (e.g. coal dust) is gasified under pressure, dust-containing gas mixtures are obtained which leave the gasifying reactor at high temperature. If the gasification is carried out as a flame reaction at temperatures above the melting point of the ash residue remaining on gasification, then it is advantageous to discharge the hot product gas together with the hot liquefied ash (i.e. slag) and thereupon to contact both the gas (for cooling purposes) and the liquid slag (for solidification and concomitant granulation) with cooling water. The direct water-cooling of the hot gas results in partial conversion of the water into steam--and in the acquisition of a certain water vapor content in the cooled product gas.
Several types of water-cooling and/or scrubbing for dust renewal are known and described in W. Strauss "Industrial Gas Cleaning", Pergamon Press, 1975 and in E. Weber/W. Brocke "Apparate der industriellen Gasreinigung", Vol. 1 "Feststoffabsclerdung", R. Oldenburg Publishes, 1973.
One prior-art approach is to use scrubbers in which water trickling or being sprayed in counterflow to the gas is made to contact the gas. The contact surface area may be increased by installing baffles or similar devices. The problem here is that relatively high specific water quantities must be used--on the order of 1-5 l/m.sup.3 gas--in order to assure proper wetting of the gas/water contact surfaces and also to keep the proportion of scrubbed-out contaminants small since otherwise such contaminants may become deposited on various surfaces and cause problems. If baffles or similar elements are not used and the water is sprayed into the gas stream, it is a frequent occurrent for scrubbed-out contaminants to foul the spray nozzles and cause uneven spray distribution. Moreover, because of the high water requirements of these devices it is customary to recycle a portion of the used scrubbing water back into the device, together with fresh water, and the contaminants contained in this recycled water tend to clog the circulation pumps and to cause corrosion of the pump parts with which they come in contact.
Other types of scrubbing equipment are also known, for example turbulent-flow scrubbers. These largely avoid the use of baffles and similar devices so as to reduce the aforementioned problems. However, they require large quantities of water and the gas/water contact is not as effective as in the previously discussed type.
Venturi scrubbers are used primarily for non-pressurized gases and suffer from the problems outlined earlier, i.e. fouling by deposition of scrubbed-out dust and erosion of the pump components due to recirculation of parts of the contaminated scrubbing water.
Rotary scrubbers are also known, which have rotating baffles or similar instrumentalities. Because of theproblems encountered with the rotating components and the electrical energy requirements for driving the same, such rotary scrubbers are used only rarely and are not known ever to have been used to scrub contaminants from gases which are under pressure.
Finally, it has been proposed to use two-stage devices--a prescrubber and a subsequently arranged venturi tube or disintegrator--to obtain cooling of the gas in conjunction with a high rate of dust removal and maximum gas saturation with water vapor. However, these devices also require a very large amount of water and the problems resulting from contamination of the device with particles scrubbed out of the gas continue to be present in them.